A portion of the disclosure including microfiche Appendix A of this patent document contains material which is subject to copyright protection. The copyright or owner has no objection to the facsimile reproduction by any-one of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all (copyright or mask work) rights whatsoever.
The present application includes a computer listing on microfiche Appendix A attached hereto. Microfiche Appendix A includes frames 1-178 disposed on 2 sheets.
The present invention relates generally to radio frequency (RF) communication systems. More particularly, the present invention relates to channel searching techniques for radio transceivers.
Radio systems are utilized in diverse applications to provide a variety of communication operations. Radio systems, such as, the commercial high-frequency (HF) data link radio, can be used to support air traffic control (ATC) and airline operational control (AOC). The HF data link radio can be used to transmit and receive voice, tactical, data, and navigational messages between aircraft and ground stations.
Radios or transceivers generally communicate messages on a channel of a communication link in accordance with a protocol associated with the communication link. For example, commercial HF data link radios or transceivers transmit and receive messages on one of about 400 channels in the frequency range between 2-30 Megahertz (MHZ). Each channel has a bandwidth of approximately 1800 bytes per second.
Commercial HF data link radios communicate ATC and AOC messages in accordance with a time division multiplexing scheme, such as, the time division multiplex access (TDMA) protocol defined in Aeronautical Radio, Inc. (Air Inc.) specification 635. The TDMA protocol allows several radios to use a single channel without interference from each other.
Conventional radio systems establish contact or connections on a channel in accordance with the protocol associated with the data link. The radio system is tuned to the appropriate channel and transmits and receives messages in accordance with the protocol. According to the commercial HF data link radio example, the airborne radio system establishes contact or connects to a base station on a particular HF frequency (e.g., channel). The radio system connects or logs on by receiving a squitter message on a particular channel and transmits information in accordance with the squitter message on the particular channel.
The particular channel (e.g., the main channel) is selected by the HF Data Link frequency search algorithm in accordance with the signal-to-noise ratios that have been experienced on the received frequencies. The HF data link frequency search algorithm attempts to choose a robust channel that will be available for the entire communication session with a ground station. Nonetheless, radio systems can have contact broken or lose the connection due to a variety of internal and external conditions. For example, an aircraft utilizing HF data link may lose contact at any time due to operational conditions of the radio system, geographic conditions (e.g., mountains and valleys), distance, weather, solar conditions, and other external situations. In radio systems, particularly HF data link radio systems utilized in aircraft applications, the amount of time during which the radio system is incapable of communicating (e.g., lost contact time) should be minimized.
In conventional voice HF operations, when the radio system loses connectivity, the radio operator must search for another channel. The search can be augmented by various products and techniques which can help the radio operator predict the availability of alternative channels (channels other than the main channel, which is no longer operational). Additionally, the skill and experience of the radio operator are extremely important when determining the availability of alternate channels. Even with a highly skilled radio operator, the time spent searching for alternate channels adversely affects the operation of the radio system. In fact, search times for alternative channels can be as long as several minutes. Once a suitable alternative channel is found, connectivity is reestablished on the alternate channel, which then becomes the main channel.
Thus, there is a need for a radio system that reduces search time associated with selecting alternate channels. Further still, there is a need for an automatic channel search algorithm that can automatically select a channel for HF data link operations, and make a list of best available alternate channels for human-operator use. Further still, there is a need for a channel selection algorithm that does not affect communication on the main channel.
The present invention relates to a transceiver apparatus for use with a high frequency (HF) radio communication system. The communication system includes channels. The communication system operates in time slots; one time slot of the time slots includes a protocol message. The transceiver apparatus includes an antenna and a control circuit coupled to the antenna. The control circuit communicates information on a selected channel in a particular time slot via the antenna in accordance with the protocol message. The control circuit receives the protocol message from at least one different channel of the channels when the information on the selected channel is not germane to the protocol operation on the selected channel. The control circuit determines the availability of the different channel in response to the protocol message from the different channel.
The present invention further still relates to a radio capable of receiving radio signals on an HF data link. The radio signals are communicated on at least a first channel, a second channel, and a third channel. The radio signals are communicated in accordance with a time division multiplex protocol including a plurality of time slots. A first squitter message is provided on the first channel in a first time slot; a second squitter message is provided on the second channel in a second time slot, and third squitter message is provided on the third channel in a third time slot. The radio includes a receiver means for receiving the radio signals and a control means for tuning the receiver means to at least the first channel, the second channel, and the third channel. The control means causes the receiver means to receive the second squitter message while the radio is waiting to communicate information on the first channel in accordance with the time division multiplex protocol. The control means monitors the availability of the second channel in response to the second squitter message. Synchronization to alternate channels is achieved more quickly in the radio.
The present invention still further relates to a method of determining availability of alternative channels on a high frequency (HF) link. The method includes receiving a main squitter message on a main channel, communicating in at least one assigned time slot on the main channel, receiving at least one alternative squitter message on at least one of the alternative channels in a non-assigned time slot, and determining the availability of the at least one alternative channel in response to the alternative squitter message.